This invention relates to the deep rolling and strengthening of fillets of crank pins of internal combustion engine crankshafts and, more particularly, to variable pressure fillet rolling of the fillets of split and arcuately offset crank pins.
Internal combustion engines conventionally have cast iron or steel crankshafts with throws incorporating integral crank pins which provide the pivot attachment points for the connecting rods coupling the pistons and the crankshaft. Since these crank pins experience high gas pressure loads and inertia forces during engine operations, their fillets are usually cold worked and hardened by deep rolling with special machinery during initial manufacture to increase their operational yield strengths. With such strengthening, there is improved crankshaft performance and service life.
With many V-block engines, adjacent and neighboring crank pin journals of the engine crankshaft are split and arcuately offset to mount the ends of connecting rods of opposing pistons in a side-by-side manner. The split pins of a V-6 crankshaft may be designed with their axes of revolution arcuately offset by an included angle of 30 degrees, for example. With such offset, each of the cylinders can be fired at 120 degree intervals or three times per crankshaft revolution to provide an even firing engine. Other angular offsets are used with other crankshafts for other internal combustion engines.
Crankshafts with such split pin design may be provided with a divider fence at the split of the pins to enable fillet rolling at the fence connecting the split-pins to one another. This fence importantly provides a thrust wall to receive side loads from the connecting rods of the pistons and strengthens the pins particularly at the overlap of the two fillets. With the fence separating the annular fillets from one another, fillets on opposite sides of the fence can be fully rolled and strengthened through 360 degrees.
The overlap of the two adjacent annular fillets in transparent end view is generally in the cross sectional shape of a football with the upper segment of the football formed by a limb of a first fillet while the lower segment is formed by a limb of the second fillet. With this overlap configuration the present invention has been devised to provide high pressure rolling and accompanying work hardening of the fillets at their overlap with backing by the offset of the pins and to provide lower pressure deep rolling of the fillets outside of the overlap to reduce distortion of the divider fence. This deep rolling importantly improves strength of the crankshaft at otherwise weakened sections necessitated for smoother engine operations.